Non-Destructive Evaluation (NDE) equipment is used to detect the presence of certain flaws, such as cracks, in various structures such as rails, airplanes, automobiles, nuclear reactor systems, pipes, etc. While most NDE equipment aims to detect the presence of such cracks, flaws, or anomalies, etc. at the surface of a structure, it is desirable to also detect their presence beneath the structure surface to more reliably identify portions of the structure at risk and to prevent failure of the structure with potentially catastrophic results. Moreover, NDE techniques traditionally identify certain flaws or defects, but do not evaluate or otherwise assess performance effects of identified potential flaws, cracks, or anomalies. Nor do they provide a mechanism for documenting a history and assessing the performance integrity of the material under test over time.
Some current NDE approaches utilize ultrasonic techniques, but these ultrasonic techniques typically require context scanning of the material under test. Ultrasonic NDE techniques generally scan the material with ultrasonic energy and monitor the reflected, scattered, or transmitted sound energy. Other NDE approaches use infrared thermal energy by imaging a sample surface that is flash-heated and the decay of the surface temperature is monitored by an infrared camera. Drawbacks with thermal imaging include the need for flash-heating the test material, often requiring coating the test material, and also the need for expensive and sophisticated thermal imaging and processing equipment. Thermographic techniques are also not particularly effective with respect to detecting deep, subsurface flaws or relatively small surface flaws. Radiographic NDE techniques typically radiate the material using X-rays, but the accuracy of radiographic techniques is generally less than satisfactory for small defects, and the radiation source poses a health/safety risk.
There is also a question about the reliability of ultrasonic, thermal imaging, and radiographic NDE techniques. For example, in the context of a railway application, it must be appreciated that conventional rail inspection in a railway system is based on ultrasonic pulse echo technology using wheel-launched acoustic energy at specific propagation angles to achieve insonification of the rail. Nevertheless, there are thousands of rail incidents per year, some costing millions of dollars. And although these NDE techniques may be workable in a laboratory environment or for small amounts of material to be tested, they are less practical when it comes to testing materials in the field or large quantities of material, e.g., miles of railway tracks, piping, etc. NDE performance may also be adversely effected by dirt, grease, corrosion, chemical reactions, etc. on the surface layer of the material to be tested.